I would like to call for a place to list some little things that surprise you about Lion. There are so many articles and lists of all the new features with information overload, I would rather focus this spot of the site on tiny delights with a note why it makes a difference to you.

Please one topic per answer, this isn't a race to enumerate everything that changed. This isn't the place for massive topics like the implications of FileVault 2 on your entire workflow - just a stroll past some little gems, fun oddities or subtle changes specific to Lion.

Answers must relate to why or how you use the feature - links to official tips and tutorials are great, but the intent is to collect little gems that affect how the system gets used. Expect answers that are not specific to lion or lack a personal use case to be heavily edited or deleted.

Use a date in Mail.app to make a quick iCal event

I just saw something while reading TidBITs in Mail. When you hover over a date, a dashed outline appears around it. When clicked, it pops up a window like this, which allows you too add an event to iCal with this date and the email subject. It's pretty useful!

Launchpad

This feature migrated from iOS brings the home screen of iOS to the mac.

I have a few applications that I do not want sitting in the dock as they aren't used often. But I hated having to go through finder to find them. With Launchpad, I can tap a button which opens up a swiping iOS style menu where I can easily find an app I want to use, and open it with just the one click.

Pinch to Zoom

Snow Leopard had this feature, but it didn't work in every application. With Lion, this works in pretty much every application. A major one for me is Final Cut Pro. Being able to pinch to zoom makes video editing so much easier.

Use Keyboard to Control Slideshow Screensaver

In the slideshow screen saver, pressing the space bar or arrow keys pauses and navigates between the pictures in the slideshow.

In Snow Leopard, I can't count the number of times I saw a picture in the screen saver I loved that I wanted to look at more closely or go back to. When I accidentally found this in Lion, it literally made me smile.

For apps you've installed from the Mac App store, you'll notice an "X" to delete them from launchpad, just like on iOS. Presumably that uninstalls them from launchpad (though they are saved in your Mac App store account).
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Joel GlovierSep 24 '11 at 13:17

The three finger drag is confusing

The three-finger-drag gesture does what it says it will, not what I thought it would.

What I expected:

Put three fingers on the trackpad, move them, the window under the cursor moves.

What happens:

Put three fingers on the trackpad, move them, the window under the cursor acts as if you have click-and-dragged. If the cursor was on Mail you might drag an email around. If it was on Safari, you drag some text snippet or image about.

To actually move a window, you need to move the cursor to the title bar and then drag with three fingers.

I thought it would be a nice meta-way to move "a thing I am working on" out of the way like shuffling paper on a desk. It's not, and I find it just as clunky as double-tap-drag. Try moving around in Google Street View with it, for instance.

Mail defaults to date sort by most recent

In Mail, when creating new mailboxes/folders, the emails are now sorted by default by date in descending order, i.e. freshest email first. Previously, you had to switch from ascending to descending, so from reverse chronological order to chronological order, for every new folder/mailbox created. A small change that made me smile and is most welcome!

so I don't want Lion, nor any subsquent version of Mac OS X,

Generally, OS X has decent memory management. But a minor annoyance that many have noticed is that, when watching in Activity Monitor while using Applications over time, the inactive memory will begin increasing, and while the system will eventually return that memory to free memory, when it does this is arbitrary and not consistent. The result is there are times when Applications need more memory, and while it should be available, instead of the system immediately returning inactive memory to the system, the application will squeeze what ever it is doing in the available memory without doing so.

The purpose of the purge command is detailed in its man page that I linked above, but a side-effect of running it is that all inactive memory will be returned to free memory. So running purge in the Terminal is a manual way for a user to free up that inactive memory.

Technically, the command first appeared in 10.6 Snow Leopard, but only if you installed the Developer Tools (xcode_3.2.6_and_ios_sdk_4.3.dmg), which is what I did to avoid the temptation of upgrading unnecessarily.

realistic New Text-To-Speech Voices

I found them to be quite amazing, especially Emily, Jill, Samantha, and Tom. Samantha, btw, is the same as the voice of Siri. I found upgrading difficult to resist for these alone, until I discovered how to install these new voices in Snow Leopard, which thankfully has entirely quelled this irrational temptation to upgrade.

Pretty much System-wide, Lion introduced the ability to take applications full-screen, hiding the Dock, the Menu Bar, and other applications. But there are only two applications that I really wanted to use full-screen.

full-screen Safari

Thankfully, Apple released Safari 5.1 for Snow Leopard, and that was one less temptation to upgrade.

full-screen Terminal

This was the one last temptation to upgrade to Lion, and the strongest one. I was envious for a long time of this single and long-time functionality available to users of Windows and its command prompt (cmd.exe). When this feature was revealed in Lion, I nearly fell out of my chair. I was only able to duplicate this functionality in Snow Leopard after discovering iTerm2. But the MacPorts port of iTerm2 was no longer supported in Snow Leopard, and the build would fail immediately. So I edited the Portfile for the iTerm2 port to allow it to build. I'll explain how I did this for other Snow Leopard lovers below:

How to build iTerm2 on Snow Leopard using MacPorts

MacPorts

MacPorts is a robust, stable, mature and easy to use package management solution, for OS X. It is modeled after FreeBSD's ports system, which has been adopted as the basis of NetBSD's pkgsrc.

install Xcode 3.2.6 for Snow Leopard

MacPorts requires an appropriate version of xcode; xcode_3.2.6_and_ios_sdk_4.3.dmg is the most recent version for Snow Leopard (after registerring for a free developer account, and logging into developer.apple.com, that link will begin your xcode download). Once the download completes, open your Terminal.app and complete the installation: